The normally, functioning heart of dogs will be maintained by extracorporeal circuit perfusing the coronary arteries. The heart, itself, pumps an optically clear liquid having the physical characteristics of blood. Thus experimental arrangement allows the interior of the living, beating heart to be visualized, photographed with color, cine-film and permits intracardiac fluid dynamics to be measured with precision. The use of synchronized, color cinephotography, intracardiac chamber pressure curves, visualization of intracardiac flow patterns by particle dispersion and intracardiac phonocardiography allows the relationship of valvular activity to propulsion of fluid in the heart and generation of cardiac sounds to be studied with, heretofore, unavailable accuracy. This data will increase knowledge of the normal, intracardiac, physiologic function of valves and their supporting structures. The experimental model will also be used to critically evaluate the function of valvular prostheses previously implanted in the heart. The information acquired from these studies will be used in the modification of existing artificial valves and in the design of completely new ones.